Radio frequency identification (RFID) is a well-established technology utilized in inventory management, security, logistics, product marketing as well as next generation smart flexible sensor platforms. This work reports the development of printed, wearable graphene temperature sensor on flexible textile substrates with structural configuration of RFID coil. Patterning of graphene in the form of sensing RFID coils on textile surfaces was achieved with cost-effective and scalable spray printing of graphene oxide and sequential reduction to reduced graphene oxide. Graphene RFID coil operating at 13.56 MHz with temperature sensing capability, are printed on flexible, ordinary fabrics to enable wearable and flexible electronics applications. The demonstration of reduced graphene oxide on textile as temperature sensitive layer is the distinct feature of this work. Good sensitivity of 0.0125°C ⁻¹ is achieved with linear response in the range of 25°C to 45°C and ~12% decrease in resistance was observed over the measured temperature span. Induced voltage of 100 mV peak-to-peak at an area of 30.25 cm ² is measured. RFID performance of the sensor coil under different bending radii starting from fully flat (0°) to complete bending (90°) was also studied, showing that sensor coil performs well during flat operation (100 mV) and stays above noise floor even under fully bended condition (12 mV). Finally, flexible temperature sensing RFID antenna attached to human body to investigate performance for wearable applications, indicating that the sensor can effectively monitor temperatures in the range of 25°C to 45°C.

This article introduces a novel method of laser ablation patterning-based additive manufacturing (AM) to develop a broadband planar antenna for sub-6 GHz wireless communications applications. The presented technique consists of fused deposition modeling (FDM) and the laser ablation cutting-based metal patterning. The metal layer is transferred to a thermoplastic-based ABS substrate without any postprocessing. FDM and metal patterning are independent operations in our procedure and therefore the proposed prototyping is time-efficient compared to the current AM techniques. The 3-D printed antenna is in the form of the single-layer ABS substrate–metal radiator fed by a coplanar waveguide (CPW). The antenna is also printed on an FR-4 substrate using printed circuit board (PCB) technology, and the radiation skills of the 3-D printed antenna are benchmarked with its PCB counterpart. The numerical results obtained with a full-wave analysis tool are verified by the experimental results. The proposed antenna operates on a broadband covering 2.54–5.84-GHz band with the peak gain around 4 dBi and meets the requirements of the Worldwide Interoperability for Microwave Access (WiMAX) and wireless local area network (WLAN) band applications. The fabricated 3D-printed antenna is loaded to human body, and the reflection coefficients are measured for off-body communication links. The calculated electromagnetic power density profiles on the human phantom are demonstrated for various operating frequencies.

We present a flexible pH sensor which leverages the unique properties of reduced graphene oxide/polyaniline (rGO/PANI) composite films through an efficient and scalable hybrid microfabrication approach, wherein the rGO/PANI films are conformally coated on flexible polyethylene terephthalate (PET) substrates via dip-coating and thereafter lithographically patterned into precise arrays of interdigitated electrodes (IDEs), serving both as the pH-active medium and the electrical interface. Upon dip-coating, a thermal reduction process is performed to yield uniform rGO/PANI composite layers on PET substrates, where the PANI content is adjusted to 20% to optimize conductivity and protonation-driven response. Composition optimization is first performed using inkjet-printed silver (Ag) contacts and a conductometric readout mechanism is employed to explore pH-dependent behavior. Subsequently, IDE arrays are defined in the rGO/PANI using photolithography and oxygen-plasma etching, demonstrating clean pattern transfer and dimensional control on flexible substrates. Eliminating separate contact metals in the final design simplifies the stack and reduces cost. A set of IDE geometries is evaluated through I–V measurements in buffers of different pH values, revealing a consistent, monotonic change in electrical characteristics with pH and geometry-tunable response. The present study demonstrated that the most precise pH measurement was achieved with an 80:20 rGO/PANI composition within the pH 2–10 range. These results establish rGO/PANI IDEs as a scalable route to low-cost, miniaturized, and mechanically compliant pH sensors for field and in-line monitoring applications.

Using Finite Difference Time Domain (FDTD) simulations, we demonstrate the effectiveness of a photonic nanojet emerging from an SiO2 sphere semi-immersed in SU-8 material under 365 nm plane wave illumination for scanning skin malignancies.

In this paper, a novel polarization insensitive metamaterial absorber using sunflower shaped unit cell is proposed. The performance of the proposed absorber was demonstrated with 3D full-wave EM solver under normal incidence for TE and TM polarization modes. Due to the symmetric geometry of the sunflower shaped unit cell, the proposed absorber provides a high level of absorptivity, about %90, for both TE and TM modes at 11.9 GHz. To enhance the absorptivity, we then created a hollow at the center of the proposed unit cell. The later device resonates at 11.7 GHz, and provides perfect absorption for both polarization modes. Our study reveals that employing hollow type symmetrical gaps provokes the interaction of EM wave and the metamaterial, and can lead to the perfect metamaterials for X-band absorber applications.